76 ' 



ujjou the Hour of the pericardiuLii (lig-. 1-J, Aur. C). The 

 heart beat is slow, an average of about twenty-five to 

 thirty contractions per minute. It is necessary to inject 

 the blood system to follow its course, and owing to the 

 fact that the digestive gland is of a very dark colour, 

 whilst the visceral mass is, on the other hand, of a light 

 tint, injections must be made with both light and dark 

 colours, in order to determine the course of the blood 

 vessels in all parts of the body. 



A great jiart of the vascular system can be made out 

 by using an injection mass formed of a mixture of lard, 

 linseed oil, and yellow oil paint (chrome yellow, as sold 

 in collapsible tubes, will do very well), in such a 

 consistency that it will run fairly easy (a little less 

 viscous than glycerine). Care must be taken not to have 

 any solid particles left in the coloured mass. It is 

 necessary to prepare the specimens, for it is useless 

 attempting to inject the living animal since the 

 contraction of the muscles closes up the vessels. The 

 necessary state of muscular relaxation can be produced by 

 placing the animals in a bucket of sea water and adding 

 slowly, at intervals, to the surface some of the following 

 mixture : — 100 c.c. 75 per cent, alcohol, 100 c.c. glycerine, 

 and 200 c.c. sea water. In about eighteen to twenty-four 

 hours, the specimens were narcotised and could be 

 transferred to formalin (5 per cent, solution) for about 

 half an hour without further contraction ; they were then 

 ready for injection. For the arterial system, the best 

 j)oint of attack was found to be the efferent l)ranchial 

 vessel (fig. 16, Br. eff.), in the ctenidial axis, with the 

 point of the syringe directed towards the heart. This 

 will inject ihe anterior and posterior aortae, the adductor 

 artery, and in fact the whole of the arterial system, 

 together with the mantle or pallial vein. 



